Data packet transmission is a communication mode generally used in a modern communications system. A transmit end sends a data packet to a receive end through a transmission link. However, transmission congestion or a transmission error on a transmission link may cause a data packet loss. The transmission link discards a data packet that fails to be sent when transmission congestion occurs on the transmission link, that is, a data packet sending demand is beyond a transport capability of the transmission link. In this case, to ensure quality of a communications service, a method of flow control is generally used to reduce a data packet loss. When a transmission error occurs on the transmission link, for example, the transmission link experiences interference, an error occurs on all or partial bits of a data packet, and the receive end discards an erroneous data packet, which results in a data packet loss. In this case, a data packet loss can be reduced by means of reducing interference. A severity level of a data packet loss can be indicated by a loss packet ratio (LPR), and the LPR can be calculated by a quantity of data packets sent by a transmit end and a quantity of data packets received by a receive end.
In other approaches, usually the LPR is directly used for determining a congestion status of a transmission link. However, since a data packet loss on a transmission link may be caused by congestion or a transmission error, it is inaccurate to determine the congestion status only by the LPR, and the congestion status of the transmission link cannot be accurately reflected, which causes inaccuracy of flow control and affects quality of a communications service.